Question

I’m building a method to get the DisplayAttribute from System.ComponentModel.DataAnnotations to show on a label for the property.

[Display(Name="First Name")]
public string FirstName { get; set; }

The method is working well:

string GetDisplay(Type dataType, string property)
{
    PropertyInfo propInfo = dataType.GetProperty(property);
    DisplayAttribute attr = propInfo.GetCustomAttributes(false).OfType<DisplayAttribute>().FirstOrDefault();

    return (attr == null) ? propInfo.Name : attr.Name;
}

The call of method can be:

lblNome.Text = GetDisplay(typeof(Person), "FirstName") + ":";

I can use a more elegant sintax using Generics, like:

string GetDisplay<T>(string property)
{
    PropertyInfo propInfo = typeof(T).GetProperty(property);
    DisplayAttribute attr = propInfo.GetCustomAttributes(false).OfType<DisplayAttribute>().FirstOrDefault();

    return (attr == null) ? propInfo.Name : attr.Name;
}

And the call:

GetDisplay<Person>("FirstName");

So, I would like to make it more more elegant using lambda expressions turning the call like this:

GetDisplay<Person>(p => p.FirstName);

The question is how can I achieve this?

Answer 1

Here is the method I use to fetch property name given by lambda expression:

    public static string PropertyName<T1, T2>(this Expression<Func<T1, T2>> expression)
    {
        MemberExpression member = null;
        if (expression.Body is MemberExpression)
            member = expression.Body as MemberExpression;
        if (expression.Body is UnaryExpression && expression.Body.NodeType == ExpressionType.Convert)
            member = ((UnaryExpression)expression.Body).Operand as MemberExpression;
        if (member == null)
            throw new ArgumentException("Selector must point to a property or field.", "expression");
        return member.Member.Name;
    }

Using this method you can just call the previous method:

string GetDisplay<T>(Expression<Func<T, object>> expression)
{
    return GetDisplay<T>(expression.PropertyName());
}